<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>自定义函数</title>
		<script>
			function add(a,b=100){
				return a+b;
			}
			alert(add(5,6));
			alert(add(6));
			alert(add("fff","dog"));
		</script>
	</head>
	<body>
	</body>
</html>